With the rapid advance of nano/micro-electromechanical systems (NMEMS) technology, there are increasing demands for innovative devices and methods capable of performing an inspection or measurement upon microstructures with high precision. Accordingly, those conventional contacted or non-contacted measurements are no longer considered to be effective enough in operation speed and precision for satisfying the demanding needs in modern measurement technologies. Moreover, in response to the improvement in our production industries, the requirement of automatic optical inspection equipment is increasing. The automatic optical inspection (AOI) equipment, being a powerful tool for assessing workmanship, can greatly enhance inspection repeatability, accuracy and throughput comparing with the use of those conventional manual inspections. Thus, AOI plays a vital role in test strategies designed to ensure the highest possible quality throughout each phase of a product's life cycle.
There has been a tremendous explosion in the popularity of confocal microscopy in recent years, due in part to the relative ease with which extremely high-quality images can be obtained from specimens prepared for conventional optical microscopy, and in its great number of applications in many areas of current research interest. Confocal microscopy offers several advantages over conventional optical microscopy, including controllable depth of field, the elimination of image degrading out-of-focus information, and the ability to collect series of optical sections from thick specimens. The key to the confocal approach is the use of spatial filtering to eliminate out-of-focus information or flare in specimens that are thicker than the plane of focus. As only one point is illuminated at a time in confocal microscopy, 2D or 3D imaging of the measured object requires scanning over a regular raster in the specimen that usually includes a fast horizontal scan in conjunction with a slower vertical scan for generating optical sections of different depths relating to the measured object. Thereafter, by the use of computers for performing a reconstructing process upon the obtained optical sections of different depths, an image containing information relating to the three-dimensional profile of the measured object can be obtained.
There are already many studies relating to the use of confocal microscopy, for instance, the 3-D profilometry using confocal microscopy with DMD-based fringe projection disclosed in TW Pat. Pub. No. I291013. Operationally, the aforesaid automatic surface profilometer deploys a DMD chip to project spatially encoded digital fringe patterns with dynamic light intensity, onto a measured object as the digital fringe patterns are designed with adaptive sinusoidal intensity modulation with respect to two orthogonal directions, and then use an imaging device to capture optical signals reflected from the surface of the measured object. Thereafter, the reflected optical signals are sent to a control unit where the focus indexes containing therein are analyzed so as to obtain depth information relating to the surface profile of the measured object. Thereafter, by the use of computers for performing a reconstructing process upon the obtained optical sections of different depths, an image containing information relating to the three-dimensional profile of the measured object can be obtained.
There is another confocal imaging system disclosed in U.S. Pat. No. 6,838,650. In the aforesaid confocal system, the field of view is preferably imaged onto an array image sensor and a pinhole array in a manner that multiple rows of sensing elements are provided in the array image sensor such that each row focuses on a different focus plane of the surface under inspection for enabling different focus planes of the surface to be imaged simultaneously using different rows of the area image sensor. Furthermore, U.S. Pat. No. 5,880,844 describes a hybrid confocal microscope. According to the aforesaid hybrid confocal microscope, the height of an object feature is computed according to the degree-of-focus of the images acquired by the different imaging paths as there is no image sensor attached to each of the imaging paths for acquiring images of the object. Image processing techniques are used to measure the degree-of-focus of an image acquired by a frame grabber from the image sensors of the multiple imaging paths. Thus, the variable degree-of-focus gathered from the multiple image paths and sensors are used to compute the height and, hence, the volume of the features of the object.